(1) Field of the Invention
The present invention relates to a resin composition having biodegradability and high absorbency, a nonwoven fabric made of the same, and pads comprising said fabric. More particularly, the present invention relates to a resin composition which has biodegradability, high absorbency and high water retentivity and can be made into a fiber, thereby being useful in application for sanitary products, and moreover does not cause a pollution problem.
(2) Description of the Prior Art
Generally, a high absorbent material should have 10 times or 1000 times of its own weight in absorbency. Absorbent cotton or pulp has been used for a long time as a high absorbent material. However, said materials have low absorbency, that is, about 20 times of its own weight, and furthermore have poor water retentivity so that the absorbed water therein can be removed easily under the external stress because of absorbing water in the gap of the base material by the capillary phenomenon. Also, said natural absorbent material have too limited production to satisfy the rapidly increasing demand.
Accordingly, as the result of the research of developing material having high absorbency and water retentivity which is synthesized by the artificial synthetic method, polymer a obtained by cross-linking polyvinyl alcohol, polyhydroxyethyl methacrylate, polyethylene glycol and the like was developed in 1965. However, though said polymer has been used as an absorbent resin for soil repairing material in gardening, a viscosity increasing agent of firing water and the medical insemination body and the like, said polymer can not repalce absorbent cotton or pulp because of having low absorbency of only 20-30 times of its own weight, thereby easily removing water therein under external stress.
On July, 1974 the United States Department of Agriculture Research North Laboratory developed a polymer having absorbency of about 1000 times of its own weight. Said polymer is described in detail on page 24 of Chemical Week of Jul. 21, 1974.
After that, several methods of preparing absorbent resin have been suggested as follows:
1) A method of preparing absorbent resin by copolymerization of polyacrylonitrile with starch, as shown in the U.S. Pat. No. 4,769,414;
2) A method of preparing absorbent resin by copolymerization of vinylsaccharide with methacrylic acid and methacrylic acid derivatives, as shown in the EP Patent No. 283,090;
3) A method of preparing high absorbent resin comprising sodium acrylate by using ultraviolet rays or radiochemical method, as shown in the EP Patent No. 287,970;
4) A method of preparing absorbent resin comprising acrylatecopolymer salt by using trimethyl propane triacrylate as cross-linking agent, as shown in the EP Patent No. 312,952;
5) A method of preparing high absorbent resin comprising sodium salt of 2-propeonic acid, acrylic acid, sorbitanol, etc. by using the inverse suspension polymerization method, as shown in the German Patent No. 38 23 729;
6) A method of preparing high absorbent resin by mixing polyacrylate with vinyltrimethoxysilane, as shown in the JP Patent Appln. Laying open No. 06042/1989;
7) A method of preparing absorbent resin by mixing polystyrene with polyacrylate, as shown in the JP Patent Appln. Laying open No. 98657.
However, most of the high absorbent materials prepared by said methods are made of a synthetic polymer which has no biodegradability so that they may cause the serious pollution problem. Also, said high absorbent materials have the poor process efficiency and absorbency in case of the fiber form will be significantly deteriorated as compared with the case of the particle form.